I didn't take my trainers on holiday and regretted it after two days. Luckily, I was bang next to the beach and went bare-foot running on the sand instead and absolutely loved it. Only went for 40 minutes each day but it was a nice change of scenery from the pool and made dipping back into the water afterwards very rewarding.
In addition, and as some have proved here, there is a fascination with chalking up 20,50 or 100 races. A few at my club were trying to get a few people along to 'celebrate' someone completing 100. Not sure I get that: I've run every saturday for years, and certainly more than 3 miles at a time. Didn't expect anyone to come along and hang up the bunting.
I kind of see your point but at the same time I would say that the vast majority of people who enjoy parkrun are never likely to ever finish first, win a local race, or anything to that affect, so aside from a PB the milestones of completing x number of parkruns is their own acheivement or recognition - anyone can be in the "50" or "100" club regardless of ability - plus regularly supporting a local community event so consistently is a good thing.